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Old 01-01-2013, 07:29 PM   #1
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What's better AGM or Wet Cell for inverter

First: Cost of batteries not an issue.
Second: 2000 Xantrex Modified Sine Wave Inverter/Charger
Third: Motor home is set up with four 6v house batteries, might have the possible room to modify trays and relocate starting batteries to install two more.
Fourth: Coach is mostly electric including refrigerator, convection oven. Gas is used for cook top,water heater, and occasionally the furnace.
Fifth: Coach seldom used for dry camping but is used on occasion and just trying to get through the night on inverter for the refrigerator then will recharge off the generator the next day.

Would the AGM's handle the load requirements better and recover faster than using the equivalent capacity wet cell?

I will be replacing the four house batteries in any case and the idea of Maintenance Free aspect of the AGM's is attractive. That being said if the wet cells would do a better job then wet cell's it is.
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Old 01-01-2013, 07:52 PM   #2
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Once you say cost is not an object, AGM is the answer. Period. Zero maintenance, you'll love it. I have "maintenance free" start batt's plus the house AGMs, zero corrosion or cable issues in 3 years. Batt's going strong as when they were installed.
I have four 300ah batteries & Xantrex 2000, coach came w/six 220ah. the AGMs work flawlessly. You just reset the battery type to AGM, then adjust the battery bank size till you get 80amps or better charge rate when batt's are down. To go to the 300's you need some additional head room, but they might fit in your rig; be sure to allow for the cable space on top when using the measurements from the mfgr's specs.
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Old 01-01-2013, 08:31 PM   #3
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Would love to go with the larger batteries however not enough head room to get the job done short of reworking the entire area on my Travel Supreme, but with the option of not needing to pull the batteries out to refill and clean connections I might be able to install two more of the 220 AH smaller ones to make up the height difference on the 300AH ones Do you also have an opinion on which brand of AGM's to buy?
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Old 01-01-2013, 10:30 PM   #4
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"......... Do you also have an opinion on which brand of AGM's to buy?"


Lifelines are the best. My 8D'd are 9 years old and still test fine.
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Old 01-02-2013, 02:46 AM   #5
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"......... Do you also have an opinion on which brand of AGM's to buy?"


Lifelines are the best. My 8D'd are 9 years old and still test fine.

How do you test them?
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Old 01-02-2013, 07:01 AM   #6
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Originally Posted by delcirose View Post
First: Cost of batteries not an issue.
Second: 2000 Xantrex Modified Sine Wave Inverter/Charger
Third: Motor home is set up with four 6v house batteries, might have the possible room to modify trays and relocate starting batteries to install two more.
Fourth: Coach is mostly electric including refrigerator, convection oven. Gas is used for cook top,water heater, and occasionally the furnace.
Fifth: Coach seldom used for dry camping but is used on occasion and just trying to get through the night on inverter for the refrigerator then will recharge off the generator the next day.

Would the AGM's handle the load requirements better and recover faster than using the equivalent capacity wet cell?

I will be replacing the four house batteries in any case and the idea of Maintenance Free aspect of the AGM's is attractive. That being said if the wet cells would do a better job then wet cell's it is.

For your purpose, AGM's would be best because they have a higher tolerance to high amp charging, a plus in an all electric rig.

However, an all electric rig with an MSW inverter? Reduced proficiency, and higher heat production from that, just about necessitates a true sine wave IMHO! Especially when cost is no factor.

Ed
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Old 01-02-2013, 09:24 AM   #7
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Yes, presently I have the MSW Xantrex, however that will be replaced with a magnum as much to protect the sensitive electronics in the entertainment area. I noticed that my Sharp TV is not liking the MSW very much at all.. Thanks for the direction to the lifeline batteries, I had pretty much figured that was the direction I would be heading in. Thank you all for your input.
I have been noticing that the Xantrex goes into over temp petty fast when trying to re-supply the energy removed from the batteries adding time to the recharge process. Was not sure if this was a product of the inverter or just having the wet cell batteries. I have equalized the batteries, checked them with a hydrometer, no dead cells, and they are two years old all replaced at the same time. No fun like RV fun.
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Old 01-02-2013, 11:37 AM   #8
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How do you test them?
There are a couple of ways. You can have a huge load test cell and put a load on the battery and measuring the time it takes for the battery to drop to a certain voltage. Because of the bulk of a load test cell, the more modern way is to use a tester that puts a small amount of AC voltage on the battery and measures the battery resistance. That resistance is used to determine the health of the battery
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Old 01-02-2013, 12:44 PM   #9
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We have four AGM 4D batteries and a Xantrex 2500 watt inverter charger (and a 600 watt pure sine wave inverter) on our sailboat. Works fine. We anchor out (no hookups) about 5-7 months a year.

We have four 6-volt Trojan 105 wet cell batteries and an Excel 1100 watt pure sine wave inverter on our fifth wheel trailer. Works fine. We boondock about 5-7 months a year (no hookups).

We equalize the batteries on the fifth wheel once a month and add distilled water to each cell as needed. AGMs never require that kind of maintenance.

The only real difference in an RV is price versus maintenance. On the sailboat the AGMs are good because they can't spill when the boat heels -- that's the only reason we got them on the boat.

So IMHO, I'd go with the cheaper wet cells unless you really hate the idea of equalizing and adding distilled water to the cells... the inverters don't care what you use.

Our Trojans have been in place for 4 years. The AGMs have been in place for 3 years. No signs that either needs to be replaced yet.
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Old 01-02-2013, 12:51 PM   #10
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details...

The small ac test is a non-intrusive type of test, it only can compare to other of the same size, it is NOT suitable for determining if the battery has the correct capacity.

That can only be determined by a known load for a measured time.

So if you have a known load like an inverter and portable heater, you could do some math to determine from the watts of the heater, overhead of the inverter what the load onthe battery is.

The turn it on and make some neasurements as it operates.

You would need the datasheet to determine the time that the battery would supply the load you are using to reach a test voltage, then you could determine almost exactly what the actual capacity of the battery is, of course you would need to be sure it was 100% charged, float charged for a few days.

Now for battery type for the inverter, AGM or flooded, alone does not matter.

Some engineering first is in order.

Minimum things that need to be known.
1. Expected load on the battery (maximum)
2. Expected amount of time to support the load (time for heavy loads)
3. Average load (considering lights only to inverter use)
4. Amount of time needed to support the average load
5. Charger

Once this is known you take the MAXIMUM load on the battery, if you have an inverter rated at 1000 watts, it will likely draw 1100 watts while operating at that load, this is 91 .6 amps at 12 volts.

Now you determine how long you need to support this load, say you need 3 hours, you look at the rate sheet of the battery and lookup the 3 hour rating, if the load is less than 92 amps the battery is too small.

You may need to parallel batteries to meet the need.

The extra loads such as lighting will be below the 8 hour rating of the battery suitable to run the inverter, so add the estimated time the lesser loads are needed by multiplying the load inamps by the time in hours to get the amp hours needed and simply add that to the size determined for the inverter.

So if you need a pair of 150 amp hour batteries to run the inverter and you also need another 40 amp hours to run the lights, then look for a pair of 170 amp hour MINIMUM batteries, so a pair of 8D size may work.

Once you determine the battery to be used then you can figure out where to place it.

This is where the AGM/VRLA is superior to the flooded, you can place them anywhere.

If you have a booth dinete the drawers under the benches likely are shorter than the benches to not hit the cabinets on the opposide side.

The space betweenthe back of the drawer and the wall are prime spaces for VRLA batteries as they can be rated for indoor use with occupied spaces, you need to check the specific battery here, but you can place the batteries here, and the inverter as close as possible to insure minimal cable losses, that part of the topic is well covered in this forum, search wire size for inverter for that.

The larger battery may not fit here, but you can parallel smaller ones of same model to build up the size.

When doing this, divide the total load bythe number of parallel batteries and use that number inthe rate sheet, the load now is called "load be string"

Good luck, others will now add their comments, do not be afraid to ask more questions as answers WILL save you time, money and frustration, and keep us all informed.
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Old 01-02-2013, 03:52 PM   #11
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People say AGM has a lower internal resistance and thus can both be charged and discharged faster and that they can go below 50 percent with suffering major damage (I am highly skeptical of that last)

however with 4 Golf car batteries... None of this matters. The two pair can provide power faster than a 2KW inverter needs, and can accept a charge faster than the inverter's charger module can pump out.

AGM are, however, maintenance free. Some folks prefer that.

Myself, i'd stay with flooded wet, but that has more to do with cost, you said cost is no object so .. It truly is up to you, AGM are Maintenence free. if cost was no object, That might well be.
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Old 01-03-2013, 02:22 AM   #12
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AGMs are the low maintenance trouble free batteries with a long life and can be used in any position. That is why I use 4 Lifeline 400 AH GPL-L16T in my 2012 Bay Star 2901. The battery bank provides 800 AH, lies flat on the 11" side over the Ford chassis frame rails on a 1" plywood bed, and are connected via 0000 (4 ought) cables. They weigh about 120 pounds each and I expect them to stay there untouched with clean connections for 10 to 12 years. My MS 2800 Magnum charger can deliver 125 amps of charging power, I have seen up to 137 amps in cold weather. The 765 watt solar panels can output up to 60 amps in bright sun around 11:45 AM and the combined charge rate has been as high as 180 amps (generator + solar) so the battery bank reduces the run time of the generator. I use Magnum's Battery Monitor Kit and Auto Gen Start also so Death Valley and Quartzsite type boondocking are what the RV is best at. The batteries are always recharged to 100% every day with out any shore power.
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Old 01-03-2013, 09:43 AM   #13
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I admit at times to be slow on the uptake, however the phrase can be installed in any position finally hit home. So I can in effect orient these batteries on their side. The terminals do not need to be to be on top. So this will allow more flexibility in the existing space without needing to do modifications. The agm's will also not need to be pulled in and out for watering, terminal cleaning etc. Even though this comes at a cost in the end considering how they will be used and their life expectancy will these cost's not average out over say a eight to ten year life expectancy? Again as always thanks for the thoughts and input from our IRV2 family.
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Old 01-03-2013, 09:53 AM   #14
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Either will work, but if cost is not an issue AGM for sure. Less internal resistance (they charge quicker), no maintenance, can be installed in any direction etc. I'd go with the Lifeline AGMs...great batteries!
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